1. Field of the Invention
The invention concerns a switching element for a valve train of an internal combustion engine, preferably for valve deactivation, having an outer part and an inner element that is axially displaceable in a bore therein, wherein the outer part and the inner element each have at least one receptacle aligned with each other in an axially separated relative position achieved by a lost motion spring, wherein one or more movable coupling means for coupling the inner element with the outer part are applied in one of the receptacles toward the other receptacle in their positions relative to one another, wherein a first upper stop for defining the relative position is applied between the inner element and the outer part, and wherein a hydraulic lash adjuster with a pressure piston is installed in the inner element, which pressure piston is fixed against moving axially out of the inner element by a second upper stop.
2. Description of the Related Art
A switching element of this type is disclosed in DE 199 15 531 that is considered generic. This switching element is shown as a switchable cam follower for a tappet push rod drive. An upper stop for defining the relative position is realized through a piston-like element arranged in the inner element. This piston-like element projects radially outward into a longitudinal groove of the outer part. In the axially extended state of the inner element relative to the outer part, the piston-like element contacts an end of the longitudinal groove. The aim of this is to achieve an aligned positioning of a coupling bore provided in the outer part and a piston arranged in the inner element for coupling.
A drawback of this prior art is that adjustment of lash in the coupling is relatively complicated and expensive. It is clear that the receptacle in the outer part (here a coupling bore) for receiving the piston must be designed with a slight lash relative to the outer peripheral surface of the piston. This lash and a vertical-position vary from one switching element to the other depending on the manufacturing conditions. The relatively broad range of variation of this mechanical free travel in the switching elements is, however, not desirable.
Therefore, to adjust the coupling lash or keep its variance within an acceptable range, the pistons are classified for locking purposes in groups. This is extremely complicated and expensive from the manufacturing and measuring point of view. For example, switching elements must be completely assembled, the lash then measured, following which the switching element must again be disassembled and mated to a suitable coupling piston. It is equally conceivable to classify the upper stops on the longitudinal groove of the outer element.
Another upper stop is provided in the aforesaid prior art for a pressure piston of the lash adjuster and is configured as a ring.
If two pistons are provided for coupling, as is the case in DE 4,206,166, the aforesaid stop-measures prove to be nearly impossible. The aligned position of the coupling bores situated diametrically opposite each other in the inner element is realized when the two axially movable parts of the switching element make contact with the base circle of the cam. An adjustment of the coupling lash in this case is accomplished by extremely complicated manufacturing and measuring techniques by pairing suitable switching elements (in this case, cup tappets) with cam pairs or camshafts. Under certain circumstances, it is necessary to tolerate an excessive lash variation.
Thus, the object of the invention is to provide a switching element of the aforementioned type in which the stated drawbacks are eliminated by simple means.